Three-dimensional printing apparatuses that utilize a thermal expansion sheet to form three-dimensional shapes are conventionally known. Among such three-dimensional printing apparatuses, a three-dimensional printing apparatus is known in which a selectively designated section of a color image is cut out and this section is converted into a binary image or a grayscale image and printed onto the surface of the thermal expansion sheet and the radiant heat applied causes printed sections of the binary image or the grayscale image to foam expand and rise (See Japanese Patent No. 5,212,504, for example).
Note that the three-dimensional printing apparatus foam expands the printed sections of the binary image or the grayscale image causing the printed sections to rise, then forms white ink along the entire surface of the thermal expansion sheet, and finally prints an original color image.